This invention relates generally to compressors and pumps, and more particularly to improved compressors and pumps of the rotary type.
In the context of compressors, the term "rotary" signifies that compression is carried out by a structural arrangement employing circular instead of reciprocating motion. The characteristic form of existing rotary compressors is a direct-driven, positive sweeping mechanism. One well-known type of rotary compressor is the rolling ring-eccentric machine which employs a roller on a shaft-mounted eccentric, the roller surface being engaged by a spring-biased vane, which is caused to move in and out of the cylinder as the roller moves within its eccentric path.
A well-designed rotary compressor of the rolling eccentric type is relatively free from vibration and well-suited to high-speed operations. The performance of such rotary compressors is characterized by high volumetric efficiency due to the small clearance volume and corresponding low re-expansion losses inherent in their design. However, rotary compressors of the type heretofore known suffer from internal leakage which results in substantial losses and markedly reduces the efficiency of the unit.
In a rolling type compressor as well as in an eccentric piston type compressor which functions in a similar manner save that it makes use of a solid eccentric without a roller, a sliding vane serves to divide the chamber into a suction side and a high-pressure side.
But only the edge of the vane engages the moving surface of the roller while the sides of the vane do not. Their sealing, therefore, depends on close clearances or an oil film interposed between the surfaces. In a like manner, the outer cylindrical surface of the roller does not engage the inner cylindrical surface of the stator nor do the sides of the roller engage the sides of the stator. Here, also, the leakage is said to be controlled by "hydrodynamic" sealing whose major design requirements are minimum clearances and high speeds.
Effective hydrodynamic sealing is contingent on clearance, rotor speed, oil viscosity and the surface finish of the parts. But even with precisely machined parts, there is unavoidable leakage due to the presence of refrigerant diluted in the oil, which flows from the high-pressure side to the suction side of the machine. Similar internal leakage effects and a loss in efficiency are experienced with the sliding vane machine, for there, too, we find unsealed relative motion between the edges of the vanes and the cylinder walls.
Another disadvantage of existing types of rotary compressors is that one is unable to vary their capacity except by controlling rotational speed. This form of control adversely affects the efficiency of the unit.
In my above-identified copending application, there is disclosed a rotary compressor including a circular rotor eccentrically supported on a driven shaft which is coaxially disposed in a cylindrical cavity formed within a stator. The rotor acts as a crank with respect to a ring freely mounted thereon. The ring functions as a piston and is caused by the eccentric rotor crank to undergo orbital motion which cyclically moves it towards and away from the inner surface of the cylindrical stator.
The cylindrical cavity is partitioned into sealed compartments by means of divider blades. Each blade is linked to the ring and is slidable within grooves and a slot formed in the stator, the inner edge of the blade engaging the surface of the ring. As the ring-piston is driven through its orbit, it strokes into and out of each cavity compartment to vary the volume of the compartment whose confining surfaces are defined by the stator, the divider blades and the surface of the ring-piston. Each compartment is provided with a suction intake and a discharge outlet so that as the piston strokes the compartment, gas is alternately drawn in, compressed and discharged.
Also disclosed in my copending application are means to provide a compressor whose capacity may be controlled either at a constant speed or by speed control without loss of efficiency. The concern of the present invention is with an improved mechanism for effecting capacity control.
In all forms of rotary compressors wherein compression is carried out by an eccentric rotor and stator arrangement and, in particular, those that employ a freely-mounted cylindrical ring on a shaft supported eccentrically therein (referred to as the roller), the roller surface is engaged by one or more spring-biased vanes. In my copending application, linked blades are slidably mounted in grooves and slots, the roller surface having peripheral clearance with the inner cylindrical surface of the stator. Such clearance is inherent in the design to avoid interference and jamming from thermal and mechanical causes.